Light emitting diodes (LED) are, due to their relatively low energy consumption, long lifetime, and capability of electronic dimming, becoming more and more used in connection with lighting applications. LEDs are successfully used in lighting applications for general illumination such as, wash/flood lights illuminating a wide area or for generating wide light beams e.g. for the entertainment industry.
However, LEDs have not presently been successfully used in connection with light application systems where an image is created and projected towards a target surface. This is especially the case in connection with entertainment lightning, where a high demand for lumen output and high image quality are required. LED projecting systems have not yet been able to fulfill these requirements.
The light in projecting systems is generally collected into an optical gate where the image is generated, and an imaging optical system projects the gate onto a target surface. WO0198706, U.S. Pat. No. 6,227,669 and U.S. Pat. No. 6,402,347 disclose lighting systems comprising a number of LEDs arranged in a plane array where a converging lens is positioned in front of the LED in order to focus the light, for instance to illuminate a predetermined area/gate or for coupling the light from the diodes into an optical fiber.
U.S. Pat. No. 5,309,277, U.S. Pat. No. 6,227,669, WO0198706, JP2006269182 A2, EP1710493 A2, U.S. Pat. No. 6,443,594 disclose lighting systems where the light from a number of LEDs is directed towards a common focal point or focusing area, for instance by tilting the LEDs in relation to the optical axis (JP2006269182 A2, WO0198706, U.S. Pat. No. 5,309,277) or by using individually refracting means positioned in front of each LED (U.S. Pat. No. 6,443,594, U.S. Pat. No. 7,226,185B, EP1710493). WO06023180 discloses a projecting system comprising a LED array with a multiple number of LEDs where the light from the LEDs is directed towards a target area and where LEDs may be mounted to a surface of a curved base or to a surface of a plane.
U.S. Pat. No. 7,623,198B discloses a light source apparatus having a plurality of light sources different in emission wavelength from each other and a prism sheet having a plurality of mutually parallel fine elongated prisms on at least one surface thereof. Lights from the light sources enter the prism sheet through a light entrance surface of the prism sheet at a predetermined angle and output from an exit surface thereof as color-mixed exiting light. A bandpass mirror is disposed between each light source and the prism sheet to transmit light in a wavelength region emitted from the associated light source and to reflect light in the other wavelength regions.
The prior art fixtures try to increase the lumen output by adding as many light sources as possible. The consequence is, however, that the efficiency with regard to power consumption versus light output is very low. Furthermore, a large amount of light is lost as the prior art fixtures typically only couple a central part of the light of the light beams through the gate in order to provide a uniform illumination of the gate, which again reduces the efficiency. The space in light fixtures is often limited and it is difficult to fit many light sources into prior art fixtures, for instance because the optical components associated with the light sources often take up a lot of space.